Method of manufacturing ceramic tape

ABSTRACT

A method of manufacturing ceramic tape includes a step of directing a tape of partially-sintered ceramic into a furnace. The tape is partially-sintered such that grains of the ceramic are fused to one another yet the tape still includes at least 10% porosity by volume, where the porosity refers to volume of the tape unoccupied by the ceramic. The method further includes steps of conveying the tape through the furnace and further sintering the tape as the tape is conveyed through the furnace. The porosity of the tape decreases during the further sintering step.

PRIORITY

This application is a continuation of U.S. application Ser. No.17/173,637 filed Feb. 11, 2021, which is a continuation of U.S.application Ser. No. 17/076,044 filed Oct. 21, 2020, which issued onApr. 6, 2021 as U.S. Pat. No. 10,967,539 and which is a continuation ofU.S. application Ser. No. 16/930,724 filed Jul. 16, 2020, which issuedDec. 29, 2020 as U.S. Pat. No. 10,875,212 and which is a continuation ofU.S. application Ser. No. 15/218,689 filed Jul. 25, 2016, which issuedon Sep. 8, 2020 as U.S. Pat. No. 10,766,165 and which is a continuationof International Application No. PCT/US16/39708 filed Jun. 28, 2016,which claims priority to U.S. Application No. 62/185,950 filed Jun. 29,2015, each of which is incorporated by reference herein in its entirety.

BACKGROUND

Aspects of the present disclosure generally relate to processes forsintering green tape, such as green tape including polycrystallineceramic grains bound in an organic binder, as well as sintered articles,such as ceramic sheets or tapes made from such processes.

Articles, such as thin sheets, tapes, or ribbons of ceramic have manypotential uses, such as serving as waveguides, when the ceramic istransmissive to light, serving as substrates that may be coated orlaminated, and integrated in batteries and other components, or otherapplications. Such articles may be manufactured by forming large ingotsof the sintered material, cutting slivers or plates of the material, andpolishing the corresponding articles to a desired form and surfacequality. Polishing helps to remove flaws or defects on the surfaces ofthe articles, but is time- and resource-consuming.

Such articles may also be manufactured by tape casting, gel casting, orother processes that include sintering of green tapes, such as strips ofinorganic grains bound in an organic binder. The green tapes aretypically placed upon a surface, called a setter board, and placedinside a furnace that burns off the organic binder and sinters theinorganic grains. The setter board is typically formed from a refractorymaterial that can withstand the sintering process. The setter boardsupports the tape when the binder is removed.

Applicants have observed that sintering causes a green tape to contract,dragging portions of itself across the setter board during thecontraction. A result is that the supported side of the resultingsintered article has surface defects, such as drag grooves, sintereddebris, impurity patches, etc. transferred from refractory material ofthe setter board to the sintering article. FIGS. 1 and 2 show examplesof surface defects 112, 212 on sintered ceramic articles 110, 210, suchas defects caused by a setter board during sintering. Applicants believethat these defects diminish the strength of the respective article byproviding sites for stress concentrations and crack initiations.

Additionally, when manufacturing thinner and thinner sintered articles(e.g., sheets, tapes, ribbons), Applicants postulate that at some point,the sintered articles may become so thin that they are difficult if notimpossible to polish. Accordingly, for such articles, those of ordinaryskill in the art may be unable to remove surface defects induced bysetter boards during sintering or defects caused by cutting. Similarly,for thicker, yet still thin sintered articles, Applicants postulate thatat some point the articles have too much surface area to polish. Controlof conventional polishing equipment with fragile and/or thin sheets oflarge surface area may become unwieldy and/or impractical. Accordingly,thin articles, particularly those with relatively large surfaces areas,having qualities generally associated with polishing, such as flatness,smoothness, and/or defect-free surfaces, may be unattainable usingconventional manufacturing methods and/or those of ordinary skill in theart may avoid trying to manufacturing such articles due to strongdisincentives in terms of overcoming manufacturing challenges andassociated costs per article.

A need exists for equipment and manufacturing processes for makingarticles, such as tapes and sheets of polycrystalline ceramics, metals,or other materials that may be sintered, where the articles may beefficiently manufactured, such as without excessive polishing, whilealso having good mechanical properties, such as due to having fewsurface defects. Such articles may be useful as substrates such as inbatteries, on printed circuit boards, as cover sheets for displays, suchfor handheld devices, or the articles may be otherwise useful.

SUMMARY

Applicants have discovered technology that removes the setter board fromthe process of sintering green tape, where resulting sintered articlesmay be unpolished, yet may have good mechanical properties. In someembodiments, technology disclosed herein relates to a continuousmanufacturing line, where a continuous tape includes a green sectionincluding inorganic particles held by an organic binder. On themanufacturing line, the green section is directed to a first heatedlocation to burn off or char the binder, forming an unbound section ofthe same tape. Next, along the manufacturing line, the unbound sectionis run through a second heated location for at least partial sinteringof the inorganic particles. The first and second heated locations may beheated by the same or different furnaces on the manufacturing line.Additional heated locations may be on the manufacturing line to furtherprocess the tape, such as a third heated location for completing thesintering of the tape, if the tape is only partially sintered at thesecond heated location. Partial sintering at the second heated locationmay allow the tape to be tensioned for further sintering at the thirdheating location, where the tension holds the tape flat, therebyfacilitating a particularly flat sintered sheet and/or one with fewsintering-induced surface defects.

The above is in part achieved by orienting the green tape past thesecond heated location in a manner that does not require setter boardsupport for the green tape, such as vertically orienting the tape.Surprisingly, Applicant have found that the weight of the tape below theunbound section need not necessarily sever or pull apart the tape at theunbound section before the at least partial sintering occurs, despitethe binder of the tape being burned off or charred. Applicantsdiscovered that the tape is able to hold itself together long enough forat least partial sintering, without a setter board. As a result, thesintered article is free of contact-induced surface defects producedduring sintering typically caused by setter boards. Surfaces on bothsides of the sintered article are consistent with one another in termsof number of defects, and that number is low enough that the resultingsintered article may have improved mechanical properties, such asincreased tensile strength, relative to articles with more surfacedefects.

Additional features and advantages are set forth in the DetailedDescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings. It is to be understood that both theforegoing general description and the following Detailed Description aremerely exemplary, and are intended to provide an overview or frameworkto understand the nature and character of the claims.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying Figures are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments, andtogether with the Detailed Description serve to explain principles andoperations of the various embodiments. As such, the disclosure willbecome more fully understood from the following Detailed Description,taken in conjunction with the accompanying Figures, in which:

FIGS. 1 and 2 are digital images of ceramic material with surfacedefects.

FIG. 3A is a schematic diagram of a manufacturing line according to anexemplary embodiment.

FIG. 3B is a plot conceptually showing temperature versus position alongthe manufacturing line of FIG. 3A.

FIG. 4 is a cross-sectional view of a furnace according to an exemplaryembodiment.

FIG. 5 is a digital image of a manufacturing line according to anexemplary embodiment with tape being processed.

FIG. 6A is a digital image of an unpolished surface of a sinteredceramic.

FIG. 6B is a conceptual side profile of unpolished sintered ceramic.

FIG. 7A is a digital image of a polished surface of a sintered ceramic.

FIG. 7B is a conceptual side profile of polished sintered ceramic.

FIG. 8 is a perspective view of a sintered article in the form of a thinsintered tape of material, according to an exemplary embodiment.

FIG. 9 is a schematic diagram from a side view of a manufacturing lineaccording to another exemplary embodiment.

FIGS. 10-11 are perspective views of manufacturing lines according toother exemplary embodiments.

FIG. 12 is a schematic diagram of a manufacturing line, or a portionthereof, according to an exemplary embodiment.

FIG. 13 is a schematic diagram of a manufacturing line, or a portionthereof, according to another exemplary embodiment.

FIG. 14 is a schematic diagram of a manufacturing line, or a portionthereof, according to yet another exemplary embodiment.

FIG. 15 is a micrograph of a thin ceramic sheet sintered on a setterboard at 100 times magnification.

FIG. 16 is the same sheet as FIG. 15 at 500 times magnification,generally from within the dashed box shown in FIG. 15 .

FIG. 17 compares partially and fully sintered tapes, made usinginventive processes disclosed herein, overlaying dark lettering on whitepaper.

FIG. 18 compares partially and fully sintered tapes, made usinginventive processes disclosed herein, overlaying white lettering on darkpaper.

FIG. 19 is a micrograph of a thin ceramic sheet sintered using inventiveprocesses disclosed herein at 100 times magnification.

FIG. 20 is the same sheet as FIG. 19 at 500 times magnification.

FIGS. 21-22 are surface scans of a tape according to an exemplaryembodiment, with widthwise (FIG. 21 ) and lengthwise (FIG. 22 ) heightprofiles.

DETAILED DESCRIPTION

Before turning to the following Detailed Description and Figures, whichillustrate exemplary embodiments in detail, it should be understood thatthe present inventive technology is not limited to the details ormethodology set forth in the Detailed Description or illustrated in theFigures. For example, as will be understood by those of ordinary skillin the art, features and attributes associated with embodiments shown inone of the Figures or described in the text relating to one of theembodiments may well be applied to other embodiments shown in another ofthe Figures or described elsewhere in the text.

Referring to FIGS. 3A-3B, a manufacturing line 310 includes a furnacesystem 312 and a workpiece (e.g., ribbon, tape, web, line, material),such as a tape 314, shown from a side view, extending into the furnacesystem 312. The tape 314 may be routed around a curve or roller 316 anddirected toward the furnace system 312. According to an exemplaryembodiment, the furnace system 312 includes a passage 318, whichincludes a binder burn-off location B and/or a sintering location C forat least partially sintering the tape 314 after the tape has passed thebinder burn-off location B. In some embodiments, the binder burn-offlocation B is adjacent to the sintering location C, such as directlyabove or below the sintering location C along the manufacturing line310, such as within 1 meter, within 50 centimeters, within 10centimeters. As will be discussed further, close placement of the binderburn-off location B and the sintering location C reduces the time/lengththat the tape 314 is unbound by binder prior to sintering.

According to an exemplary embodiment, the passage 318 of the furnacesystem 312 is oriented so that the tape 314 may extend generallyvertically through the passage 318, such as without contacting surfaces320 of at least sections of the furnace system 312 directed to burningoff binder (e.g., binder burn-off location B) and/or at least partiallysintering the tape 314 (e.g., sintering location C). For example, thepassage 318 may be oriented so that the tape 314 may extend generallyvertically, and move upward and/or downward along a path that isoriented between 45 and 135 degrees relative to horizontal, such asbetween 60 and 120 degrees, such as at 90 degrees plus or minus 10degrees. Passing the tape 314 through the binder burn-off location Band/or a sintering location C, without contacting the tape 314 withsurfaces 320 of the sintering location C and/or surfaces 322 of thebinder burn-off location B, is believed to improve the surface qualityof the tape 314 as it is processed by the furnace system 312, byreducing material transfer and/or scoring or otherwise shaping of thetape 314 via contact.

According to an exemplary embodiment, a first section of the tape 314 isa green tape section 314A, which may be positioned at a location A alongthe manufacturing line 310. According to an exemplary embodiment, thegreen tape section 314A includes polycrystalline ceramic and/or minerals(e.g., alumina, zirconia, lithium garnet, spinel) bound by an organicbinder (e.g., polyvinyl butyral, dibutyl phthalate, polyalkyl carbonate,acrylic polymers, polyesters, silicones, etc.). In contemplatedembodiments, the green tape section 314A may include metal particlesbound in an organic binder. In other contemplated embodiments, the greentape section 314A may include glass grains (e.g., high purity silicagrains, borosilicate, aluminosilicate, soda lime) or other inorganicgrains bound by an organic binder. In contemplated embodiments, thegreen tape section 314A may include glass-ceramic particles (e.g.cordierite, LAS lithium aluminosilicates, Nasicon structure lithiummetal phosphates, celsian) bound in an organic binder. According to anexemplary embodiment, the green tape section 314A has a porosity of fromabout 0.01 to about 25 vol % and/or the inorganic particles have amedian particle size diameter of from 50 to 1,000 nanometers and aBrunauer, Emmett and Teller (BET) surface area of from 2 to 30 m²/g. Inother contemplated embodiments, the above materials may be bound byinorganic binders or other binders and/or the above materials may beotherwise sized or have other porosity.

As the green tape section 314A passes the binder burn-off location B,the furnace system 312 is configured to burn off and/or char, due tooxidation, volatilization, and/or cross-link, binder material from thegreen tape section 314A, such as most of the binder, such as at least90% of the binder. According to an exemplary embodiment, the green tapesection 314A is self-supported through the burn-off location B and neednot and/or does not contact surfaces 322 of the burn-off location B.

Beyond the binder burn-off location B, the tape 314 is no longer “green”and a second section of the tape 314 is a unbound tape section 314B(e.g., burned-off tape section, charred binder tape section), which maybe unsintered, yet may be without binder or with charred binder. Becausethe unbound tape section 314B is without working and/or un-charredbinder, one of ordinary skill in the art may expect the unbound tapesection 314B to simply collapse or fall apart under its own weight orweight of portions of the tape 314 below the unbound tape section 314B,such as due to lack of binder. However Applicants have discovered thatthe unbound tape section 314B may remain intact, despite the binderbeing burned off and/or charred, if the tape 314 is properly handled,such as if tension on the tape 314 is controlled and/or if the tape 314is not bent and/or reoriented prior to at least partial sintering ofinorganic material (e.g. ceramic grains) of the tape 314.

Referring still to FIG. 3A, the unbound tape section 314B portion of thetape 314 then passes into and/or by the sintering location C, and thefurnace system 312 is configured to at least partially sinter thepolycrystalline ceramic or other inorganic material of the unbound tapesection 314B. For example, polycrystalline ceramic grains may besintered such that the grains bond or fuse to one another yet the tape314 still includes a large amount of porosity (e.g., at least 10% byvolume, at least 30% by volume), where the “porosity” refers to theportions of the volume of the tape unoccupied by the inorganic material,such as the polycrystalline ceramic.

Once at least partially sintered, the corresponding section of the tape314 is an at least partially sintered tape section 314C. Partially andnot fully sintering the at least partially sintered tape section 314Cmay increase the strength of the tape 314 to the extent that tension maybe applied to the tape 314 to facilitate subsequent shaping of the tape314. According to an exemplary embodiment, under tension, additionalsintering of the tape 314 occurs to produce a particularly flat orotherwise-shaped sintered article (see generally FIG. 5 ).

According to an exemplary embodiment, the manufacturing line 310 furtherincludes a tension regulator 324, which influences tension in the tape314, such as by directly interacting with the at least partiallysintered tape section 314C. The tension regulator 324 may control andseparate tension in the tape 314 above versus below the tensionregulator 324 such that tension may be different in the portions of thetape 314 on either side of the tension regulator 324. In someembodiments, the tension regulator 324 includes an air bearing, whereair may be directed in direction F with or against a direction G thatthe tape 314 moves through the manufacturing line 310, such as to adjusttension in the tape 314. In other embodiments, the tension regulator 324includes nip rollers that pull or push the tape 314 to influence tensionin the tape 314. In still other embodiments, the tension regulator 324may be a wheel (see, e.g., FIG. 12 ), where friction on a surface of thewheel as well as rotation of the wheel influences tension in the tape314. As discussed, tension in the tape 314 may be used to shape the tape314 as the tape 314 is sintered, such as at the sintering location C orelsewhere along the manufacturing line 310. Additionally, tension(positive or negative amounts thereof) applied to the tape 314 by thetension regulator 324 may help hold the unbound tape section 314Btogether, by influencing the tension in that section.

Referring now to FIG. 3B, temperatures of the tape 314 may vary alongthe length of the tape 314 as a function of position of the particularportion of the tape 314 along the manufacturing line 310. The green tapesection 314A, prior to entering the binder burn-off location B mayexperience a first temperature, such as room temperature (e.g., about25° C.). Near the binder burn-off location B, the temperatureexperienced by the unbound tape section 314B of the tape 314 may begreater than that experienced by the green tape section 314A, such as atleast 200° C., at least 400° C. Near and at the sintering location C,the temperature experienced by the tape 314 may be greater still thanthat experienced by the tape 314 near the binder burn-off location B,such as at least 800° C., at least 1000° C. at the sintering location C.Portions of the tape located at a position along the manufacturing line310 past the sintering location C may then experience a lowertemperature than portions of the tape 314 at the sintering location Cand/or than portions of the tape 314 at the binder burn-off location B,such as experiencing room temperature.

Referring to FIG. 4 , a furnace system 410 includes a guide 412 thatdefines a passage 414 that extends at least partially through thefurnace system 410, such as fully through a depth L1 of the furnacesystem 410. In some embodiments, the guide 412 may be a tube or shaft,which may be formed from refractory materials. According to an exemplaryembodiment, the passage 414 is generally vertically oriented such thatgravity may draw straight or otherwise act along a length of an elongateworkpiece (e.g., flexible green tape, ribbon, line; see generally tape314 of FIG. 3A) extending through the passage 414. In some applicationsof the furnace system 410, the workpiece may be narrower than thepassage 414 and may be positioned within the passage 414 so as to notcontact surfaces of the guide 412. The furnace system 410 may be used ina manufacturing line, such as the manufacturing line 310.

According to an exemplary embodiment, the passage 414 of the furnacesystem 410 has depth dimension L1 that extends through the furnacesystem 410, a width dimension (extending into and out of the FIG. 4 )orthogonal to the depth dimension L1, and a gap dimension L2 that isorthogonal to both the depth dimension L1 and the width dimension.According to an exemplary embodiment, the depth dimension L1 of thepassage 414 is greater than the width dimension, and the width dimensionis greater than the gap dimension L2. According to an exemplaryembodiment, the gap dimension L2 is at least 1 millimeter, such as atleast 2 millimeters, at least 5 millimeters, and/or no more than 500centimeters. In some embodiments, the width and gap dimensions are equalto one another such that the passage 414 is cylindrical.

Referring to FIG. 4 , the furnace system 410 includes a binder burn-offlocation B′ and a sintering location C′. The burn-off location B′ isconfigured to burn binder material from the workpiece and the sinteringlocation C′ is configured to at least partially sinter the workpiece.According to an exemplary embodiment, the furnace system 410 includes aheat source 416, such as an electric resistance heating element, gas oroil burners, or other sources of heat. In some embodiments, the heatsource 416 surrounds at least a portion of the sintering location C′and/or is separated from the burn-off location B′, such as by barriersor walls 418, which may be formed from refractory material. According toan exemplary embodiment, the heat source 416 of the furnace system 410is positioned above or below the burn-off location B′. Accordingly, heatmay synergistically pass from the sintering location C′ to the binderburn-off location B′. In other embodiments, the burn-off location B mayhave a heat source that is separated from the sintering location C′.

The workpiece, prior to entering the binder burn-off location B′ mayexperience a first temperature, such as room temperature (e.g., 25° C.).Near the binder burn-off location B′, the temperature experienced by theworkpiece may be greater than room temperature, such as at least 200°C., at least 400° C.′. As the workpiece nears and passes the sinteringlocation C′, the temperature experienced by the workpiece may be greaterstill than that experienced by workpiece near the binder burn-offlocation B′, such as at least 800° C., at least 1000° C. Portions of theworkpiece beyond the sintering location C′, on the side of the sinteringlocation C′ opposite to the binder burn-off location B′, may thenexperience a lower temperature, such as experiencing room temperature.

Referring now to FIG. 5 , a cast of 3 mole-percent Yttria-StabilizedZirconia (3YSZ) green ceramic may be produced, as described in U.S. Pat.No. 8,894,920. In one example, from the cast, a green tape 512 ofmaterial, 2.5 cm wide by 5 m long was cut. The green tape 512 was woundonto a cylindrical roller 514 and was then fed at a controlled rate of 2inches per minute into a furnace system 516, as shown in FIG. 5 (seealso furnace system 410, as shown in FIG. 4 ). The sintering location C″of the furnace system 516 was held at 1200° C. A binder burn-offlocation B″ was insulated and built out of alumina fiberboard to providea region for binder burnout. The binder burn-off location B″ was heatedby hot gasses exiting the sintering location C′ of the furnace system516.

In the configuration 510 shown, Applicants have found that a 10 inchlong binder burn-off location B″ (shown with length in the verticaldirection) allows the tape 512 to be successfully fed at up to about 3inches per minute. The sintering location C″ of the furnace system 516shown is twelve inches, resulting in a total time in the sinteringlocation C″ of about four to six minutes. At the exit of the furnacesystem 516, the 3YSZ tape 512′ is partially sintered, having a relativedensity of about 0.65. The 3YSZ tape 512′ has sufficient strength forhandling, is flexible, and is about 40 micrometers thick. As shown inFIG. 5 , several meters of sintered tape 512′ have been reoriented on asupportive plastic carrier film 518.

Applicants have found that the binder burn-off location B″ should be ata temperature in the range of about 200 to 600° C. range for polyvinylbutyral (PVB) binder. Applicants have found that sufficient length ofthis binder burn-off location B″ may also allow high tape speed throughthe furnace system 516 because if the binder burn-off location B″ tooshort, binder may be removed at an excessive rate, which may causeuncontrolled binder elimination and failure of the tape 512. Further,Applicants have found the length of the binder burn-off location B″relates to the rate at which the tape 512 may be successfully sintered.According to an exemplary embodiment, the length of the binder burn-oflocation B″ is at least 2 inches and/or no more than 50 inches, such asat least 4 inches and/or no more than 20 inches. In other contemplatedembodiments, the binder burn-off location B″ may have a length outsideof the above ranges.

Referring still to FIG. 5 , in another example, tape 512, this timealumina green ceramic, was produced and fired using configuration 510.The process of casting the tape 512 included steps of batching, milling,de-gassing (or de-airing), filtration, and tape manufacturing. Forbatching, alumina powder was mixed with a water-based tape castingingredients including a binder, a dispersant, a plasticizer, and ade-foaming agent. Ingredients used were produced by Polymer Innovations,including an acrylic-based binder that is water soluble.

For milling, the batched material was milled and mixed in a mill by, forexample: ball milling, high shear mixing, attrition milling, vibratorymilling, roller milling, and like methods. The milling stepde-agglomerates particles and creates a uniform, well-dispersed slurry.In some embodiments, Applicants found an attrition mill (also called astirred ball mill), from Union Process, may facilitate de-agglomerationby breaking up agglomerates or nano-agglomerates of alumina powder.Applicants believe the attrition mill has benefits over other millingprocesses and equipment due to high energy input to the materials duringthe milling process, which allows the batch to be milled to smallerparticle sizes in a shorter period of time compared to other techniques,for example, 1 to 3 hours versus 50 to 100 hours with ball milling.

One Union Process attrition mill used had a total volume of 750milliliters (mL) and a working volume/capacity of 250 mL. The tank wasloaded with 130 mL of slurry and 740 grams of 2 mm 99.9% pure aluminamedia (i.e., grinding media). The tank was water cooled to 15° C. duringthe milling process to avoid overheating and to reduce evaporation ofsolvent(s). The slurry was initially milled for 5 minutes at 500revolutions per minute (rpm) to break down large agglomerates, then thespeed was increased to 1300 rpm and milled for 1 hour. At the end ofmilling, the tank was slowed to 170 rpm and a de-foaming agent was addedto remove entrapped air. The slurry was then poured through a 80 to 120mesh screen to remove the milling media from the slurry beforede-gassing.

For de-gassing, such as after milling, Applicants found that the milledmedia may be strained from the slurry, and the slurry may bede-aired/de-gassed using a vacuum to remove entrapped air from themilled product that may otherwise include bubbles within the mix.De-gassing may be accomplished with a desiccator chamber and then aMazerustar vacuum planetary mixer. The slurry may be loaded into adesiccator chamber and de-gassed for up to 10 minutes. After the initialde-gassing, the slurry may be loaded into the planetary mixer andoperated under vacuum for 5 minutes. Applicants found that analternative de-gassing procedure, eliminating the Mazerustar mixer, isto use a higher vacuum in the desiccator chamber.

For filtration, the slurry was filtered to remove any large scalecontamination from the mixture. Such contaminates may otherwise giveadverse optical properties in the sintered material, for example.Filtering may be accomplished with 50 micrometers, 25 micrometers, 10micrometers, or 1 micrometer filters. Such filters may be made of, forexample, nylon, fiber, or other suitable materials.

For the tape manufacturing step, samples were cast on a silicone-coatedMylar® film, which was approximately 50 to 150 micrometers thick.Applicants find that the silicone coating provides easy release of thetape material after drying. Other suitable films for tape 512 may be,for example, Teflon®, glass, a metal belt, and like alternativematerials. To facilitate the tape manufacturing, the slurry was passedunder a doctor blade which had a gap of about 4 to 20 mils (about 100 to500 micrometers) to form a thin sheet of ceramic tape. Typically an 8mil (about 200 micrometers) blade height was used. The casting blade wasmoved across the Mylar® at a speed of 10 mm/sec. The speed may be variedas needed to increase process speed, and to modify the thickness of thetape 512. After drying, the thickness of the tape was 100 to 150micrometers. The tape 512 in this state is referred to as “green tape.”

Still referring to FIG. 5 , a 1.2 meter long by 120 micrometer thick and1.2 centimeter wide tape 512 of was cut out of the green castingdescribed above and released. The tape 512 was wound onto thecylindrical roller 514. The tape 512 was then fed at a controlled rateof 1 inch per minute into the furnace system 516, as shown in FIG. 5 .The tape 512 had sufficient strength to hold together under its ownweight during binder burn-off. The sintering location C″ of the furnacesystem 516 was maintained at a temperature of 1100 C. At the exit of thefurnace system 516, the alumina tape 512′ was partially sintered, havingrelative density of approximately 0.7. The fired thickness of the tape512′ was about 100 micrometers.

Referring to FIGS. 6A-6B, materials manufactured according to inventiveprocesses disclosed herein and with inventive equipment disclosed hereinmay be distinguished from materials manufactured according toconventional processes. According to an exemplary embodiment, a sinteredarticle 610 (e.g., sheet, foil) includes a first surface 612 (e.g., top,side) and a second surface 614 (e.g., bottom), which may be opposite tothe first surface 612. The sintered article further includes a body 616of material extending between the first and second surfaces 612, 614.

A thickness T of the article 610 may be defined as a distance betweenthe first and second surfaces 612, 614. A width of the article 610 (seegenerally width W of sintered sheet 810 of FIG. 8 ) may be defined as afirst dimension of one of the first or second surfaces 612, 614 that isorthogonal to the thickness T. A length of the article 610 (seegenerally width L of sintered sheet 810 of FIG. 8 ) may be defined as asecond dimension of one of the first or second surfaces 612, 614 that isorthogonal to both the thickness T and the width. According to anexemplary embodiment, the sintered article 610 is an elongate thin tapeof sintered material. Due at least in part to geometry, some suchembodiments are flexible, allowing the article 610 to bend around amandrel or spool (e.g., diameter of 1 meter or less, 0.7 meters orless), which may be beneficial for manufacturing, storage, etc. In otherembodiments, the sintered article 610 may be otherwise shaped, such asround, annular, sleeve- or tube-shaped, not have a constant thickness,etc.

According to an exemplary embodiment, the length of the article 610 isgreater than twice the width of the article 610, such as at least 5times, at least 10 times, at least 100 times greater. In someembodiments, the width of the article 610 is greater than twice thethickness T of the body, such as at least 5 times, at least 10 times, atleast 100 times greater. In some embodiments, the width of the article610 is at least 5 millimeters, such as at least 10 mm, such as at least50 mm. In some embodiments, the thickness T of the article 610 is nomore than 2 centimeters, such as no more than 5 millimeters, such as nomore than 2 millimeters, such as no more than 1 millimeter, such as nomore than 500 micrometers, such as no more than 200 micrometers.According to an exemplary embodiment, as green tape is passed into afurnace and allowed to sinter, the sintering occurs nearly uniformly;and length, width and thickness of the sheet may diminish up toapproximately 30%. As such, dimensions of green tape disclosed hereinmay be 30% greater than those described for the sintered articles above.Thin tapes may allow the manufacturing line to operate rapidly becauseheat from the furnace can quickly penetrate and sinter such tapes.Further thin tapes may be flexible, facilitating bends and changes indirection along the manufacturing line (see generally FIG. 11 forexample).

According to an exemplary embodiment, the sintered article 610 issubstantially unpolished such that either or both of the first andsecond surfaces 612, 614 have a granular profile, such as when viewedunder a microscope, as shown in the digital image of FIG. 6A andconceptually shown in the side view of FIG. 6B. The granular profileincludes grains 618 protruding generally outward from the body 616 witha height H (e.g., average height) of at least 25 nanometers and/or nomore than 100 micrometers relative to recessed portions of the surfaceat boundaries 620 between the grains 618, such as the height H of atleast 50 nanometers and/or no more than 80 micrometers. In otherembodiments, the height H may be otherwise sized.

The granular profile is an indicator of the process of manufacturing thesintered article 610 in that the article 610 was sintered as a thintape, as opposed to being cut from a boule, and that the respectivesurface 612, 614 has not been substantially polished. Additionally,compared to polished surfaces, the granular profile may provide benefitsto the sintered article 610 in some applications, such as scatteringlight for a backlight unit of a display, increasing surface area forgreater adhesion of a coating or for culture growth. In contemplatedembodiments, the unpolished surfaces 612, 614 have a roughness fromabout 10 to about 1000 nanometers across a distance of 10 millimeters inone dimension along the length of the article, such as from about 15 toabout 800 nanometers. In contemplated embodiments, either or both of thesurfaces 612, 614 have a roughness of from about 1 nm to about 10 μmover a distance of 1 cm along a single axis.

By contrast, the sintered article 710, of the same material as sinteredarticle 610, includes polished surfaces 712, 714, where grain boundariesare generally removed due to the polishing. In contemplated embodiments,sintered articles 610 manufactured according to the processes disclosedherein may be polished, as shown in FIGS. 7A-7B; depending upon, forexample, the particular intended use of the article. For example, use ofthe article 610 as a substrate may not require an extremely smoothsurface, and the unpolished surface of FIGS. 6A-6B may be sufficient;whereas use of the article as a mirror or as a lens may requirepolishing as shown in FIG. 7A-7B. However, as disclosed herein,polishing may be difficult for particularly thin articles or those thatare thin with large surface areas.

Applicants believe that sheets of sintered ceramic or other materialscut from boules may not have readily identifiable grain boundariespresent on surfaces thereon, in contrast to the article of FIGS. 6A-6B.Applicants further believe that boule-cut articles may typically bepolished to correct rough surfaces from the cutting. But, Applicantsbelieve that surface polishing may be particularly difficult orcumbersome for very thin articles of sintered ceramic or othermaterials, with the degree of difficulty increasing as such articles arethinner and the surface areas of such articles are larger. However,sintered articles manufactured according to the presently disclosedtechnology may be less constrained by such limitations because articlesmanufactured according to the present technology may be continuouslymanufactured in long lengths of tape. Further, dimensions of furnacesystems, as disclosed herein, may be scaled to accommodate and sinterwider articles, such as having a width of at least 2 centimeters, atleast 5 centimeters, at least 10 centimeters, at least 50 centimeters.

According to an exemplary embodiment, the sintered article 610 has agranular profile and has consistent surface quality on surfaces 612, 614thereof, which may be very different from articles manufactured usingsetter boards, as discussed in the Background, where one side istypically marked by contact (e.g., adhesions and/or abrasions) from thesetter board while the other side may not be exposed to the setterboard. In some embodiments, such as where the sintered article 610 is inthe form of a sheet or tape (see generally sheet 810 as shown in FIG. 8), the surface consistency is such that an average area of surfacedefects per square centimeter of the first surface is within plus orminus fifty percent of an average area of surface defects per squarecentimeter of the second surface, where “surface defects” are abrasionsand/or adhesions having a dimension along the respective surface of atleast 15, 10, and/or 5 micrometers, as shown in FIGS. 1-2 for example,such as within plus or minus thirty percent of an average area ofsurface defects per square centimeter of the second surface, such aswithin plus or minus twenty percent of an average area of surfacedefects per square centimeter of the second surface.

According to an exemplary embodiment, the sintered article 610 has highsurface quality, which again may be very different from articlesmanufactured using setter boards, as discussed in the Background, whereadhesions and/or abrasions from the setter board may lower surfacequality. In some embodiments, such as where the sintered article 610 isin the form of a sheet or tape (see generally sheet 810 as shown in FIG.8 ), the surface quality is such that, on average per square centimeter,the first and second surfaces both have fewer than 15, 10, and/or 5surface defects having a dimension greater than 15, 10, and/or 5micrometers, such as a fewer than 3 such surface defects on average persquare centimeter, such as fewer than one such surface defect on averageper square centimeter. Accordingly, sintered articles manufacturedaccording to inventive technologies disclosed herein may have relativelyhigh and consistent surface quality. Applicants believe that the highand consistent surface quality of the sintered article 610 facilitatesincreased strength of the article 610 by reducing sites for stressconcentrations and/or crack initiations.

According to an exemplary embodiment, the article 610, and thecorresponding material of the grains of the green tape, includespolycrystalline ceramic. According to an exemplary embodiment, thearticle 610 includes (e.g., is, consists essentially of, consists atleast 50% by weight of) zirconia, alumina, spinel (e.g., MgAl₂O₄,ZnAl₂O₄, FeAl₂O₄, MnAl₂O₄, CuFe₂O₄, MgFe₂O₄, FeCr₂O₄,), garnet,cordierite, mullite, perovskite, pyrochlore, silicon carbide, siliconnitride, boron carbide, titanium diboride, silicon alumina nitride,and/or aluminum oxynitride. In some embodiments, the article 610 is ametal. In other embodiments, the article 610 is glass sintered frompowder grains. In some embodiments, the article 610 is an IX glassand/or glass-ceramic. Materials disclosed herein may be synthetic.

Referring now to FIG. 8 , in some embodiments, a sintered article is inthe form of a sheet 810 (e.g., sintered tape) of a material disclosedherein. The sheet 810 includes a surface 814 (e.g., top or bottom) withanother surface opposite thereto and a body extending between the twosurfaces 814 (see generally sides 612, 614 and body 616 of article 610of FIGS. 6A-6B). According to an exemplary embodiment, a width W of thesheet 810 is defined as a first dimension of one of the surfaces 814orthogonal to the thickness T′. According to an exemplary embodiment,the sheet 810 has at least two generally perpendicular lengthwise sideedges 812. A length L of the sheet 810 is defined as a second dimensionof one of the top or bottom surfaces 814 orthogonal to both thethickness T′ and the width W. The length L may be greater than or equalto the width W. The width W may be greater than or equal to thethickness T′.

According to an exemplary embodiment, the thickness T′ is no more than500 micrometers, such as no more than 250 micrometers, such as no morethan 100 micrometers, and/or at least 20 nanometers. According to anexemplary embodiment, the sheet 810 has a surface area of at least 10square centimeters, such as at least 30 square centimeters, such as atleast 100 square centimeters, and even exceeding 1000, 5000, or even10,000 square centimeters in some embodiments; or is otherwise sizedaccording to geometries disclosed herein, such as with regard toembodiments of the article 610. In some embodiments, the sheet 810 has awidth W that is less than ¼, ⅕, ⅙, 1/7, ⅛, 1/9, 1/10 and/or 1/20 thelength L thereof. Such geometries may be particularly useful for certainapplications, such as for use of the sheet 810 as a substrate of arectilinear battery and/or for use of the sheet 810 as a surface forgrowing carbon nanotubes in an oven, where the sheet 810 fills surfacesof the oven, yet does not fill substantial volume of the oven.

According to an exemplary embodiment, the sheet 810 includes (e.g., isformed from, consists of, consists essentially of, consists more than50% of in volume) a material selected from the group consisting ofpolycrystalline ceramic and synthetic mineral. In other embodiments, thesheet 810 includes glass, metal or other materials, as disclosed herein.Further, according to an exemplary embodiment, the material of the sheet810 is in a sintered form such that grains of the material are fused toone another (see generally FIG. 6A). The sheet 810 may have a granularprofile (see generally FIGS. 6A-6B) or may be polished (see generallyFIGS. 7A-7B).

For example, in some embodiments, the sheet 810 is made from aluminapowder having a median particle size diameter of from 50 to 1000nanometers and a BET surface area of from 2 to 30 m²/g. The sheet 810 ismade from a tape-casted alumina powder of from 99.5 to 99.995 weightpercent alumina and from about 100 to about 1000 parts per million of asintering additive, such as magnesium oxide. In some embodiments, thesheet 810 is translucent. The sheet 810 may have a total transmittanceof at least 30% at wavelengths from about 300 nm to about 800 nm whenthe sheet 810 has a thickness of 500 μm or less. In some embodiments,the total transmission through the sheet 810 is from about 50% to about85% at wavelengths from about 300 nm to about 800 nm when the sheet 810has a thickness of 500 μm or less. In some embodiments, diffusetransmission through the sheet 810 is from about 10% to about 60% atwavelengths from about 300 nm to about 800 nm when the sheet has athickness of 500 μm or less. In contemplated embodiments, the sheet 810may have the above-disclosed transmittance percentages with a wavelengthin the above-disclosed ranges but with other thicknesses, such as otherthicknesses disclosed herein. Materials disclosed herein other thanalumina may also result in such a translucent sintered article.

Referring to FIG. 9 , a manufacturing line 910 includes a source 912 ofgreen tape 922, a furnace system 914, tension regulators 916, 918, and areceiver 920 of sintered tape 924. According to an exemplary embodiment,the source 912 of green tape 922 may be in the form of a roll of thegreen tape 922, as may be separately manufactured. From the source 912,the green tape 922 is directed into a first portion 926 of the furnacesystem 914 such as by way of a guiding passage 928. As shown in FIG. 9 ,in some embodiments, the green tape 922 is directed along a verticalaxis through the furnace system 914 such that the green tape 922 doesnot contact a setter board and/or surfaces of the furnace system 914.

The first portion 926 of the furnace system 914 may include a binderburn-off location (see generally location B of the manufacturing line ofFIG. 3 ) and a location for partial sintering of the tape 912 (seegenerally location C of the manufacturing line of FIG. 3 ). Accordingly,tape 932 exiting the first portion 926 of the first system 914 may bepartially sintered. Tension in the tape 922 through the first portion926 of the furnace system 914 may be influenced by the tension regulator916, which may differentiate tension in the tape 922, 932, 924 on eitherside of the tension regulator 916 along the manufacturing line 910. Asshown in FIG. 9 , below the tension regulator 916 the furnace system 914includes a second portion 930.

According to an exemplary embodiment, tension in the tape 932, 924between the tension regulators 916, 918 may be greater than tension inthe tape 922, 932, 924 not between the tension regulators 916, 918. Insome embodiments, increased tension between the tension regulators 916,918 may be used to hold the tape 932 flat as the tape 932 is sintered inthe second portion 930 of the furnace system 914. For example, partiallysintered tape 932 may be flexible enough to bend and/or flatten bytension in the tape 932 between the tension regulators 932, 918, yet thepartially sintered tape 932, due to the bonds of partial sintering, maybe strong enough to support the tension without failure. Put anotherway, in the second portion 930 of the furnace system 914, the partiallysintered tape 932 is sintered to a final density and held under enoughtension to flatten the sheet, tape or ribbon, eliminating curl, warp,camber, etc. that may appear with unconstrained sintering. For example,Applicants found a 1 centimeter wide partially-sintered ribbon ofzirconia or alumina was able to support greater than 1 kilogram oftension, about 20 megapascals, without failure.

Accordingly, referring once more to FIG. 8 , in contemplatedembodiments, the unmodified surface of the sheet 810 has a flatness offrom about 0.1 μm to about 50 μm over a distance of 1 cm along a singleaxis, such as along the length of the sheet 810. Such flatness, incombination with the surface quality, surface consistency, large area,thin thickness, and/or material properties of materials disclosedherein, may allow sheets, substrates, sintered tapes, articles, etc. tobe particularly useful for various applications, such as tough coversheets for displays, high-temperature substrates, flexible separators,and other applications.

Due to limited ability of garnet to creep or relax under pressure load,garnet may be difficult to reshape after the garnet has beenmanufactured. Accordingly, garnet may be difficult to manufacture thinand flat according to conventional processes. To do so, those of skillin the art have typically sandwiched green bodies between flatrefractory surfaces, which typically results in many surface defects onboth sides of the sintered article. Accordingly, the presently disclosedtechnology is believed to be particularly useful when manufacturing thinsheets of synthetic garnet as disclosed herein.

Referring to FIG. 10 , a manufacturing line 1010, similar tomanufacturing line 910 of FIG. 9 , includes a source 1012 of green tape1022, a furnace system 1014 having two separate portions 1026, 1030,tension regulators 1016, 1018, and a receiver 1020 of sintered tape1024. However, with the manufacturing line 1010, the green tape iscontinuously manufactured on the line 1010. Further, the sintered tape1024 is cut into strips 1032 (e.g., at least 5 centimeters long, atleast 10 centimeters long, and/or no more than 5 meters long, no morethan 3 meters long) as the sintered tape 1024 emerges from the secondportion 1030 of the furnace system 1014. The strips 1032 subsequentlymay be stacked, packaged, and shipped.

Referring to FIG. 11 , a manufacturing line 1110 includes a source oftape 1112 (e.g., green tape). The source is in the form of a spool 1114of the tape 1112, where the tape 1112 is initially on a polymericbacking 1116, such as Mylar. As the tape 1112 comes, generallyhorizontally, off the spool 1114 (e.g., within 30-degrees of horizontal,within 10-degrees of horizontal), the polymeric backing 1116 is pulledoff the tape 1112 at a separation location 1118 and wound onto aseparate spool 1120. The tape 1112 then passes over an air bearing 1122and is gradually redirected, with a controlled amount of sag, into afirst guide 1124, which orients the tape 1112 generally vertically(e.g., within 30-degrees of vertical, within 10-degrees of vertical).

Following the first guide 1124, the tape 1112, in a green form, movesupward into a first furnace 1126 (see generally furnace 410 as shown inFIG. 4 ). In some embodiments, the first furnace 1126 is a lowertemperature furnace that chars or burns organic binder off of the tape1112 to form an unbound section of the tape 1112. The first furnace 1126may also partially sinter the resulting unbound section of the tape1112, to form a partially sintered section 1128 of the tape 1112. Afterpassing through the first furnace, the tape 1112 may be directed througha second guide 1130. The first and second guides 1124 1130 align thetape 1112 with a passage through the first furnace 1126 so that the tape1112 does not contact surfaces of the first furnace 1126, therebyreducing the number of adhesion and abrasion related surface defects.Such a tape 1112 may still have some defects, such as due to contactwith errant particles, etc.

According to an exemplary embodiment, following the second guide 1130,the partially sintered section 1128 of the tape is routed over a wheel1132. In some embodiments, the wheel 1132 has a low-friction surface1134, over which the partially sintered section 1128 slides. Atemperature differential between the wheel 1132 and the partiallysintered section 1128 may help inhibit sticking or adhesion between thewheel 1132 and the partially sintered section 1128. According to anexemplary embodiment, the wheel 1132 rotates to control tension in thetape 1112, such as by providing different tension in the tape 1112 oneither side of the wheel 1132.

For example, in some instances, the wheel 1132 rotates (e.g., clockwise)against the direction (e.g., counter-clockwise) that the tape 1112slides over the wheel 1132, decreasing tension in the tape 1112 on theside of the wheel 1132 from which the tape 1112 is coming and increasingtension in the tape 1112 on the side of the wheel 1132 to which the tape1112 is going, with the increased tension being maintained on a distalend of the tape 1112 by a tension regulator, such as a spool receivingthe tape 1112 (see generally FIGS. 3 and 9 ), a robotic arm drawing thetape 1112 (see generally FIG. 10 ), rollers, etc. Tension in the tape1112 as the tape 1112 passes through a second, possibly highertemperature, furnace 1136, holds the tape 1112 flat as the tape 1112 isfully sintered.

The construction and arrangements of the manufacturing line, equipment,and resulting sintered articles, as shown in the various exemplaryembodiments, are illustrative only. Although only a few embodiments havebeen described in detail in this disclosure, many modifications arepossible (e.g., variations in sizes, dimensions, structures, shapes, andproportions of the various elements, values of parameters, mountingarrangements, use of materials, colors, orientations) without materiallydeparting from the novel teachings and advantages of the subject matterdescribed herein. Some elements shown as integrally formed may beconstructed of multiple parts or elements, the position of elements maybe reversed or otherwise varied, and the nature or number of discreteelements or positions may be altered or varied. The order or sequence ofany process, logical algorithm, or method steps may be varied orre-sequenced according to alternative embodiments. Other substitutions,modifications, changes and omissions may also be made in the design,operating conditions and arrangement of the various exemplaryembodiments without departing from the scope of the present inventivetechnology.

Referring momentarily again to FIG. 6 , the granular profile includesgrains 618 protruding generally outward from the body 616 with a heightH (e.g., average height) of at least 5 nanometers, such as at least 10nanometers, such as at least 20 nanometers, such as at least 25nanometers and/or no more than 200 micrometers, such as no more than 100micrometers, no more than 80 micrometers no more than 50 micrometersrelative to recessed portions of the surface at boundaries 620 betweenthe grains 618.

Referring to FIG. 12 , a manufacturing line 1210 for partial sinteringincludes a source of tape 1212 (e.g., green tape). The source is in theform of a spool 1214 of the tape 1212, where the tape 1212 is initiallyon a polymeric backing 1216, such as Mylar. In some such embodiments,the tape 1212 comes off the spool 1214 and over a roller 1244 and avacuum hug drum 1242, then the polymeric backing 1216 is pulled off thetape 1212 at a separation location 1218 and is tensioned by a tensiondevice 1240, passing over a roller 1246 and wound onto a separate spool1220. The tape 1212 (without backing 1216) then passes into the binderburnout section B′″ of the furnace 1226. In some such embodiments, thetape 1212 enters oriented generally vertically and/or without contactingthe furnace 1226.

Following the separation location 1218, the tape 1212, in a green form,moves downward into the furnace 1226 (see also generally furnace 410, asshown in FIG. 4 ). In some embodiments, the binder burn out section B′″of furnace 1226 is a lower temperature furnace that chars or burnsorganic binder off of the tape 1212 to form an unbound section of thetape 1212. A higher temperature portion C′″ of the furnace 1226 may alsopartially sinter the resulting unbound section of the tape 1212, to forma partially sintered section 1228 of the tape 1212, shown in FIG. 12passing out of the furnace 1226.

After passing through the furnace 1226, the tape 1212 may be directeddrawn across a roller 1252 that acts as second guide. The separationlocation 1218 and exit roller 1252 may align the tape 1212 with apassage through the furnace 1226 so that the tape 1212 does not contactsurfaces of the furnace 1226, thereby reducing the number of adhesionand abrasion related surface defects. According to an exemplaryembodiment, the separation location 1218 and roller 1252 or other guideat or near an exit of the furnace 1226 are generally vertically alignedwith one another, such as along a line that is within 15-degrees ofvertical, such as within 10-degrees.

Applicants note that such a tape 1212 may still have some defects, suchas due to contact with errant particles, particles in the air, etc. Theexit roller 1252 may be made of a low friction polymeric material. Afterpassing over the exit roller 1252, the partially sintered tape can bewound on a receiving spool 1250.

Example 1

A 90 foot long tape of partially sintered zirconia tape was made with anapparatus generally as shown in FIG. 12 . The green tape was made inmanner similar to that described in U.S. Pat. No. 8,894,920 B2 usingTosho (Japan) zirconia powder 3YE. The green tape was cast at a widthlarger than about 20 cm and thickness of the green tape was about 25micrometers. The tape was then manually slit to about 15 mm in widthusing circular razor blades. The green tape was passed from a pay-outspool (see generally spool 1214 in FIG. 12 ) over the separationlocation (see separation location 1218 in FIG. 12 ) and through a binderburn-out chimney (see burn-out section B′″ of furnace 1226 in FIG. 12 ),through a transition zone (see zone X′″ in FIG. 12 ) and into a highertemperature furnace (e.g., section C′″ of the furnace 1226 in FIG. 12 ).

Referring to the Example 1 in the context of FIG. 12 , at the separationlocation, 1218, the ceramic tape 1212 was released from the carrier film1216. The carrier film 1216 was run over a tensioning device 1240 and onto a take-up spool 1220. The binder-burn out zone B′″ was passivelyheated by hot air from the furnace section C′″. The channel in thefurnace and binder burnout chimney used for Example 1 was made fromceramic fiber board in parallel plates with a gap of between 0.125 and0.5 inches between the plates (see generally gap 414 and L2 of FIG. 4 ).The width of the channel orthogonal to the gap was about 3.5 inches. Thelength of the binder burnout zone was about 17 inches and the length ofthe furnace below the binder burnout zone was 24 inches.

Applicants note that the green tape can be threaded into the furnaceeither cold or hot. If threading hot, Applicants set a temperature near1000° C. for the furnace and a tape speed of 1 inch/min, when sinteringor partially sintering 3YSZ, 3 mol % yttria-stabilize zirconia,tetragonal-phase zirconia polycrystal “TZP”, and/or alumina or otherceramics with similar sintering temperatures. After threading hot, afterthe tape comes out of the bottom of the furnace, the temperature can beincreased and the speed of the tape increased. If threading cold,Applicants recommend moving (i.e., transporting, conveying) the tape ata low speed, 0.25 to 1 inch/min., during heat up through the furnace.

In this Example 1, the tape was threaded hot, and after threading, thefurnace was heated to and set at 1200 C, and the tape was then moved ata speed of 8 inches/min. through the furnace. The binder burnout chimneywas at a temperature of between about 100 to 400° C. The green tape wastransported through the furnace for was over 2.25 hours, and about 90feet of continuous length of partially sintered tape was obtained.

Sintering shrinkage in the width was about 9.5-10.5%. The partiallysintered tape was rolled on a 3.25 inch diameter spool without cracking.

Example 2

A 65 foot length of partially sintered zirconia tape was made with anapparatus similar to that shown in FIG. 12 , where the green tape wasagain made in manner similar to that described in U.S. Pat. No.8,894,920 using Tosho (Japan) Zirconia powder 3YE. The green tape wascast at a width larger than about 20 cm. The thickness of the green tapewas about 25 micrometers. The green tape was then manually slit to about52 mm in width using circular razor blades.

Next, the green tape was passed from the pay-out spool over theseparation location and through a binder burn-out chimney, through atransition zone, and into a higher temperature, actively-heated furnace(e.g., furnace 1226). The binder-burn out zone was passively heated byheated air from the furnace. The channel in the furnace and binderburnout chimney was (again) made from ceramic fiber board in parallelplates with a gap of between ⅛ and ½ inch between the plates. The widthof the channel was about 3½ inches. The length of the binder burnoutzone was about 17 inches and the length of the furnace was 24 inches.

In this Example 2, after threading, the furnace was heated to 1000° C.,1025° C., 1050° C., 1075° C., and 1100° C. while the tape was moved at aspeed of 2 inches/min. therethrough. The binder burnout chimney was at atemperature of between about 100 and 400° C. Tape was run at theindividual furnace temperatures for about an hour for each temperature.The furnace was run for over 6.5 hours, and over continuous 65 feet(green) of partially sintered tape was run through the furnace.

Sintering shrinkage across the width of the tape was dependent onfurnace temperature and, as listed in the following Table 1. Some out ofplane deformation was encountered and variation of the sinteringshrinkage in the Table is partially due to the out of plane deformationof the tape.

TABLE 1 52 mm Green Tape Temperature Shrinkage % 1000° C. 2.08% 1000° C.1.56% 1025° C. 2.34% 1050° C. 3.47% 1075° C. 4.28% 1100° C. 5.61%

In various embodiments disclosed herein, such as for materials andsystems disclosed herein, the temperature of the higher-temperaturefurnace is at least 800° C., such as at least 1000° C. Green tap ispassed therethrough at a rate of at least 1 inch/min, such as at least 2inch/min. Rate may be increased by increasing the length of the furnace,for example. Shrinkage of green tape passing therethrough was at least1.5%, such, as at least 2% in some embodiments and/or no more than 20%,such as no more than 15%.

Example 3

About a 60 foot length of partially sintered zirconia tape was made withan apparatus, similar to that shown in FIG. 12 , where the green tapewas again made in manner similar to that described in U.S. Pat. No.8,894,920 using Tosho (Japan) zirconia powder 3YE. The green tape wascast at a width larger than about 20 cm. The thickness of the green tapewas about 25 micrometers. The tape was then manually slit to about 35 mmin width using circular razor blades.

The green tape was passed from the pay-out spool over the separationlocation and through a binder burn-out chimney, through a transitionzone and into the furnace. The binder-burn out zone was passively heatedby heated air from the furnace. The channel in the furnace and binderburnout chimney was made from ceramic fiber board in parallel plateswith a gap of between ⅛ and ½ inch between the plates. The width of thechannel was about 3½ inches. The length of the binder burnout zone wasabout 17 inches and the length of the furnace was 24 inches.

In this Example 3, after threading, the furnace was heated to 1100° C.,1150° C. and 1200° C. while the tape was moved at a speed of 4 and 6inches/minute. The binder burnout chimney was at a temperature ofbetween about 100° C. and 400° C. About ten feet of the tape at eachtemperature and respective tape speed condition was spooled on to a 3.25diameter spool after partial sintering, without breaking.

Sintering shrinkage was measured and is listed in the following Table 2,where some out of plane deformation was encountered and variation of thesintering shrinkage in the Table is partially due to the out of planedeformation of the tape.

TABLE 2 Temp Speed Shrinkage (° C.) (in/min) Percent 35 mm green width1100 4 5.05 1100 6 5.16 1150 4 8.09 1150 6 6.73 1200 4 12.01 1200 611.20

Example 4

A 175 foot length of partially sintered zirconia tape was made with anapparatus shown in FIG. 12 . Zirconia green tape was made as describedabove, but tape was manually slit to about 15 mm width using circularrazor blades. The tape was passed from the pay-out spool over theseparation location and through a binder burn-out chimney, through atransition zone and into the furnace. Temperatures of 1100° C. to 1200°C. and speeds of 4, 6, or 8 inches/min. were run. The binder burnoutchimney was at a temperature of between about 100 and 400° C., and atotal of 175 feet (green) of partially sintered tape was made.

Sintering shrinkage was measured and is listed in the following Table 3,where some out of plane deformation was encountered and the variation ofthe sintering shrinkage in the table is partially due to the out ofplane deformation of the tape. Tape made at 1200 C and 8 inches perminute, had an average out of plane flatness over the length and widthof the tape, of about 0.6 mm overall, when measured over 1200 mm alongthe length of the tape.

TABLE 3 Temp Speed Shrinkage (° C.) (IPM) Percent 15 mm green width 11004 5.38 1100 6 6.70 1100 8 5.07 1150 4 8.58 1150 6 8.16 1150 8 7.25 12004 11.89 1200 6 11.33 1200 8 10.07

Example 5

A 147 foot length of partially sintered zirconia tape was made with anapparatus similar to that shown in FIG. 12 . Zirconia green tape wasmade as described above and slit to about 15 mm using circular razorblades. The tape was processed as described above, except where, afterthreading, the furnace was heated to and set at 1200° C., and the tapewas moved at a speed of 8 inches/minute. The binder burnout chimney wasat a temperature of between about 100° C. and 400° C. The green tape wasmoved through the furnace for over 3 hours, and over 147 feet ofcontinuous length (green) of partially sintered tape was obtained.

Referring now to FIG. 13 , a manufacturing line 1310 for partialsintering includes a source of partially sintered tape 1312. The sourceis in the form of a spool 1314 of the partially sintered tape 1312,where the tape 1312 may have an interleaf material. As the tape 1312comes off the spool 1314 and over a roller 1342. Plates 1346 of hightemperature material form a narrow channel in the furnace 1326.

The tape 1212 then passes into the furnace 1326, the tape 1312 beinggenerally vertical and/or without contacting the furnace and/or withoutcontacting the furnace along a central portion thereof. In contemplatedembodiments, edges of the tape may contact guides or surfaces in thefurnace, but may later be removed to provide a low-defect center portionof the tape, as disclosed herein. In some such embodiments, thelengthwise edges of the tape include indicia of cutting, such as laseror mechanical marks.

After passing through the furnace 1326, the final sintered tape 1329 maybe drawn across a tension device 1340. The input roller 1342 and tensiondevice, 1340, are generally linearly-aligned with the channel throughthe furnace 1326 so that the tape 1312 does not contact surfaces of thefurnace 1326, in some such embodiments, thereby reducing the number ofadhesion- and abrasion-related surface defects as described herein.After passing over the tension device 1340 the final sintered tapepasses over two rollers 1344, and through a conveyance device 1360(e.g., rollers, bearing, treads). After the conveyance device 1360 thefinal sintered tape can be spooled with or without interleaf material.

Referring to FIG. 14 , a manufacturing line 1410 for partial sinteringincludes a source of partially sintered tape 1412. The source is in theform of a spool 1414 of the partially sintered tape 1412, where the tape1412 may have an interleaf material. As the tape 1412 comes off thespool 1414 the tape 1212 then passes into the furnace 1426, the tape1412 being generally vertically oriented. A tensioner (e.g., weight1460, rollers), is attached to the partially sintered tape to draw thetape and/or hold the tape flat during the sintering. In contemplatedembodiments, the weight 1460 may be a length of the tape itself.

Surprisingly, as disclosed above, Applicants have found that a shortlength of the green tape, with the binder burned out, can support sometension, without the tape falling apart. The tensile strength of thesection with burned-out binder, but prior to entering thehigher-temperature furnace, is just a fraction of the tensile strengthof ideal, fully-sintered tape of the same material and formed from agreen tape of the same dimensions and composition, such as less than20%, such as less than 10%, such as less than 5%, but is still positive,such as at least 0.05%.

Example 6

Partially sintered tape of 15 mm (green) width was made as described inExample 1. A roll of this partially sintered tape, 15 mm wide (green),about 25 micrometers thick (green), was then put on the apparatussimilar to system 1310 shown in FIG. 13 (e.g., second furnace, secondsintering location). The ceramic plates, 1346, were made of siliconcarbide. The gap between the plates was 2 to 8 mm and the width of theplates was 4 inches. The outside dimension of the furnace was 21 incheslong. The furnace was heated to 1400 C (e.g., at least 100° C. greatertemperature than the furnace of Example 1, such as at least 200° C.greater, 400° C. greater).

In Example 6, the partially sintered tape (from Example 1) was rapidlythreaded by hand into the 1400° C. furnace at greater than 1foot/minute. Enough tape was provided from the spool 1314 that the tape1312 was wound around the tensioning device 1340, through two rollers1344, and through a conveyance device 1360.

After threading, the tape was run at 2 inches per minute. Less than 50grams of tension was put on the sintering tape by the tension device1340. About 9 inches of dense, final sintered tape was produced (see,e.g., fully sintered tape 2010 of FIGS. 17-22 ). The tape wastranslucent, text could be read through it if the text was placed incontact with the tape (see fully sintered tape 2010 of FIGS. 17-18 andcompare to partially sintered tape 2012 of FIGS. 17-18 ). The tape didhave some white haze from light scattering, probably from a slightporosity (e.g., porosity less than 1%, such as less than 0.5%, and/or atleast 0.1%).

Cross tape shrinkage was about 24%. Batch fired material of the sametype of tape casting had a sintering shrinkage of about 23%, +/−about0.5%. Although the partially sintered tape used for this experiment hadsome out of plane deformation, after final sintering, the tape was flatin the direction of tape motion. There was some “C-shaped” curl in thecross web (tape) direction. An area of 1 cm×1 cm of the fully sinteredtape was examined by optical microscopy at 100-times magnification. Bothsides of the final sintered tape were examined. No adhesion or abrasiondefects typical of setter boards were found.

As seen in FIG. 15 , the final sintered tape can be bent to a radius ofless than about, 2.5 cm

Example 7

A second-stage sintering apparatus, similar to that shown in FIG. 14 wasused. The furnace was only about 4 inches high, with a 2-inch hot zone.Partially sintered tape of 30 mm wide (green) was used that was made inmanner similar that described for Example 3. Prior to partial sintering,the tape was about 25 micrometers thick. A spool of the partiallysintered tape was put over the furnace, where the furnace had a narrowgap of 3/16th of an inch and 3.5 inches wide in the top and bottomfurnace insulation, to allow the tape to pass through. The tape wasthreaded cold through the gaps and a weight of 7.5 grams was attached(see generally FIG. 14 ). The furnace was heated to 1450° C., and tapemotion was started when the furnace achieved 1450° C. The tape was runfrom top to bottom at a speed of 0.5 inches per minute. About 18 inchesof fully-sintered sintered zirconia tape was made. The zirconia tape wastranslucent. In Example 7, with the 4 inch furnace, the tape, as well asthe fully sintered portion thereof, was longer than the furnace.

Referring to FIGS. 15-16 , for context and comparison purposes, greentape (3 mol % yttria-stabilize zirconia) was made as described in theabove Examples and sintered using conventional sintering processes,including use of an alumina setter board to support the green tapeduring the sintering, to form a ceramic tape 3010. Surface defects dueto adhesion and abrasion from the setter board can be seen at 100-timesmagnification, as shown in FIG. 15 . Many of the adhesion orabrasion-caused defects form pin holes 3012 in the sintered sheetbecause the sheet is so thin, on the order of 25 micrometers. As shownin FIG. 15 , the defects due to adhesion and abrasion from the setterboard are generally oblong in a common direction to one another.

As discussed above, setter-induced defects are typically surfacefeatures caused by sintering shrinkage of a green tape in contact with asetter board, where the ceramic drags portions of itself across thesetter board during sintering shrinkage. The result is that thesupported side of the resulting sintered article has surface defects,such as drag grooves, sintered debris, impurity patches, etc.transferred from refractory material of the setter board to thesintering article, and pits in the surface where the setters pull outmaterial from the sintered article. Minimizing such setter defects isimportant when the ceramic article is has thin films deposited on it. Ifthe layer thickness of the thin film or films is similar to a setterdefect dimension, the thin film may have pin holes or have the setterdefect traversing the thin film layer(s).

Compare the ceramic tape 3010 of FIGS. 15-16 , to the ceramic tape 2010of FIGS. 17-22 , manufactured using the technology of the presentdisclosure; especially as shown in FIGS. 19-20 , which are at the samemagnifications 100 x and 500 x, respectively, of FIGS. 15-16 , and arefrom a green tape made in the same way as the tape used for FIGS. 15-16. More specifically, the ceramic tape 2010 was continuously sintered, asdisclosed herein, run at 1400° C. at a rate of 2 inches per minutethrough a secondary furnace as described in the Examples, with a siliconcarbide central channel. Comparing ceramic tape 3010 to ceramic tape2010, both tapes show various indicia of casting at the surface, such aselongate, rolling stria and sloping (hills/valleys). The ceramic tape3010 shows numerous setter-related defects: bonded particles, pull-outand setter-drag defects, such as where setter drag producescharacteristic damage patterns in regions due to gouging of the surfaceas the shrinking tape drags across the setter surface, as discussedherein.

Referring to FIGS. 15-16 and FIGS. 19-20 , bonded particles, larger than5 μm in a cross-sectional dimension thereof, were easily observed at100× in optical examination of the surfaces (see FIGS. 15 and 19 ). Morespecifically, across an area of about 8 cm′, one such particle wasobserved on the surface of the ceramic tape 2010 sintered using thetechnology disclosed herein, while across an equal area of about 8 cm′,eight such particles were observed on the surface of the ceramic tape3010. Applicants believe the ceramic tape 3010 had more bound particlesdue to contact with the setter, while the ceramic tape 2010 had asmaller number of bound surface particles, which may have been presentdue to adhesion of particles in the furnace atmosphere. This smallnumber of bound surface particles on the ceramic tape 2010 may befurther reduced in future process embodiments that use filters or otherprocesses to remove or reduce particles in the furnace atmosphere.

According to an exemplary embodiment, tape manufactured according to thepresent disclosure has, on average over the surface thereof, fewer than5 bonded particles, larger than 5 μm in a cross-sectional dimensionthereof, per 8 cm², such as fewer than 3 such particles, such as fewerthan 2 such particles.

According to an exemplary embodiment, a sheet of sintered ceramic, asdisclosed herein, has a thickness of less than 50 micrometer and fewerthan 10 pin holes, having a cross-sectional area of at least a squaremicrometer (or fewer than 10 pin holes over the full surface, if thesurface area is less than a square micrometer), per square millimeter ofsurface on average over the full surface, such as fewer than 5 pinholes, fewer than 2 pin holes, and even fewer than fewer than 1 pin holeper square millimeter of surface on average over the full surface.

Referring to FIGS. 19-20 , the ceramic tape 19 has a granular surfacewith bulges 2014. The bulges have longest dimensions on the order of 100or more micrometers. The bulges are generally oblong, such as havingmajor axes oriented generally in the same direction as one another, suchas 90% within 15-degrees of a direction D, such as within 10-degrees.The bulges may be distinguished from setter-induced surface defects,such as abrasion and adhesion, because the bulges are generally smoothlyrolling and continuously curving from adjoining surface, as opposed tobeing defined by or including disjointed or discontinuous borders on asurface as is characteristic of an adhered particle or an abrasioncaused by a setter. The bulges may be indicia of at least some processesdisclosed herein, such as due to the less-constrained sinteringprocesses. Other embodiments may not include such bulges, such as if thetape is tensioned axially and widthwise during sintering, which may bedone via tensioners (e.g., rollers, treads, wheels, mechanicaltensioners or other such elements).

Referring now to FIGS. 21-22 , a ceramic tape 4010 has been manufacturedaccording to the processes disclosed herein, without a setter board. Thematerial of the tape 4010 is 3 mol % yttria-stabilize zirconia,tetragonal-phase zirconia polycrystal “TZP.” The width of the tape isbetween 12.8 to 12.9 mm. The portion shown is from a 22 inch long pieceof tape. The thickness of the tape is about 22 micrometers.Incidentally, the white spots are marker markings on the tape that thescanner did not recognize.

For comparison purposes, the tape was fully sintered below the line, andonly partially sintered above the dashed line L. SEC1, SEC2, SEC3, SEC4are profiles of the top surface of the ceramic tape 4010. The profilesshow that the tape has some “C-shaped” curvature about the lengthwiseaxis (shown as X-axis in FIG. 21 ). The camber in the tape is decreasedby fully sintering, under tension, as disclosed herein. As can be seen,maximum height of the tape decreased by about 100% from about 1.68 mm tobetween 0.89 and 0.63 mm. Applicants believe that through presentprocesses and/or further process refinements, such as increased tensionor changing process speeds, that the maximum height of thefully-sintered tape resting flat on a flat surface would be less than1.5 mm, such as less than 1 mm, such as less than 0.7 mm, such asideally less than about 100 micrometers, such as for a tape having awidth of about 10 to 15 mm.

In contemplated embodiments, the tapes described herein may be wound ona spool, as shown in the Figures, to form a roll of tape. The spool mayhave a diameter of at least about 0.5 cm, such as at least about 2.5 cm,and/or no greater than 1 m, with the length of the tape being at least 1m, such as at least 10 m, and having a width and thickness as describedherein, and/or such as a width of at least 10 mm and/or no greater than20 cm and a thickness of at least 10 micrometers and/or no greater than500 micrometers, such as no greater than 250 micrometers, such as nogreater than 100 micrometers, such as no greater than 50 micrometers.

What is claimed is:
 1. A method of manufacturing ceramic tape,comprising: directing a tape of partially-sintered ceramic into afurnace, wherein the tape is partially-sintered such that grains of theceramic are fused to one another yet the tape still includes at least10% porosity by volume, where the porosity refers to volume of the tapeunoccupied by the ceramic; conveying the tape through the furnace; andfurther sintering the tape as the tape is conveyed through the furnace,wherein the porosity of the tape decreases during the further sintering.2. The method of claim 1, further comprising drawing the tape ofpartially-sintered ceramic from a source prior to directing the tapeinto the furnace.
 3. The method of claim 2, wherein the source is aspool of the tape of partially-sintered ceramic.
 4. The method of claim1, further comprising applying tension to the tape during the furthersintering.
 5. The method of claim 4, further comprising holding the tapeflat with the tension during the further sintering.
 6. The method ofclaim 5, wherein the tension comprises 20 megapascals.
 7. The method ofclaim 1, following the further sintering, further comprising winding thetape on a spool.
 8. The method of claim 7, wherein the spool has adiameter of at least 0.5 cm.
 9. The method of claim 8, wherein length ofthe tape on the spool is at least 10 m, width is at least 10 mm, andthickness is at least 10 μm.
 10. The method of claim 9, wherein thewidth is no greater than 20 cm and the thickness is no greater than 500μm.
 11. The method of claim 1, wherein, during the further sintering,temperatures experienced by portions of the tape in the furnace are atleast 800° C., while other portions of the tape outside the furnace areexperiencing lower temperatures.
 12. The method of claim 11, wherein theother portions of the tape outside of the furnace are experiencing roomtemperature.
 13. The method of claim 1, wherein the porosity of the tapeafter the further sintering is less than 1%.
 14. The method of claim 1,wherein the ceramic comprises alumina, zirconia, lithium garnet, and/orspinel.
 15. The method of claim 1, wherein the tape is conveyed throughthe furnace at a rate of at least 1 inch per minute.
 16. The method ofclaim 1, wherein, as the tape is directed into the furnace, the tapestill includes at least 30% porosity by volume.
 17. A method ofmanufacturing ceramic tape, comprising: drawing a tape ofpartially-sintered ceramic from a source, wherein the tape ispartially-sintered such that grains of the ceramic are fused to oneanother yet the tape still includes at least 10% porosity by volume,where the porosity refers to volume of the tape unoccupied by theceramic; directing the tape of partially-sintered ceramic into afurnace, conveying the tape through the furnace; further sintering thetape as the tape is conveyed through the furnace, wherein the porosityof the tape decreases during the further sintering; and applying tensionto the tape during the further sintering.
 18. The method of claim 17,wherein the tension comprises 20 megapascals.
 19. A method ofmanufacturing ceramic tape, comprising: directing a tape ofpartially-sintered ceramic into a furnace, wherein the tape ispartially-sintered such that grains of the ceramic are fused to oneanother yet the tape still includes at least 10% porosity by volume,where the porosity refers to volume of the tape unoccupied by theceramic, wherein the ceramic comprises alumina, zirconia, lithiumgarnet, and/or spinel; conveying the tape through the furnace; andfurther sintering the tape as the tape is conveyed through the furnace,wherein the porosity of the tape decreases during the further sintering,wherein length of the tape is at least 10 m, width of the tape is atleast 10 mm, and thickness of the tape is at least 10 μm.
 20. The methodof claim 19, wherein the width is no greater than 20 cm and thethickness is no greater than 500 μm.